How do we know self-righteousness is dangerous?

Self-righteousness is dangerous because it fosters a false sense of security in one's own works rather than dependence on Christ’s righteousness. The Pharisees prided themselves on moral behavior and religious observance yet were condemned by Jesus for their spiritual blindness. They shut up the kingdom of heaven against themselves and others, believing their adherence to law was sufficient for salvation. Scripture teaches that Christ is the end of the law for righteousness to all who believe, implying that embracing self-righteousness instead of reliance on His grace can lead to eternal peril.